welcome to the site, & thanks for your service
NOW a few things
first off FLOORING a new motor is never a GOOD way to break one in, and hate to say it but long life ain't going to happen if you run it full throttle often either?>
the noise your hearing is is a rev limiter, its designed to electronically shut down excessive RPMS
to prevent motor damage, more common when a person try's to go faster in a lower gear and hits MAX rpms and then the limiter kicks in to control things
if you wanted a FAST atv, sorry you bought the wrong atv here, honda are SLOW as to about ever other 4x4 atv out there, there made more for work than play, in basic terms!
so, NO its NOT going to get better as time goes by, your hitting max speeds already with it and thats all she wrote?
and NO fix really to it either, a programmer and a exhaust will just spend your money and do little to things, more than make it louder!
again, this is NOT a fast atv period, or a very spirited like trail machine, Honda is m,ore the slow and steady type of atv LOL
as for helmets, there are tons out there, all have some better features than others, its your head, I suggest buy a decent priced model that fits IT best!
I like full face helmets, and goggles, IMO they are the best for all seasons and protection is very good!
best way to BUY a helmet IMO is GO try them on, as NO 2 makers seem to make them same size or fit
a helmet should be sung NOT loose to work right!
you can GO to a GOOD atv/MX store and try on some model and then go surf the web for best deals
closeout's on last yrs models can save you 50% or more on costs?